The present invention concerns a method for connecting a liquid crystal display to a printed circuit, particularly the printed circuit carrying the electronic components of a digital display, in a timepiece.
A liquid crystal display (LCD) includes, in a known manner, outside the sealing frame of two transparent substrates of the same dimension, paths for connecting the electrodes of the display to a printed circuit board (PCB) that, to the best of the Applicant""s knowledge, always has a substantially plane surface. This connection is currently achieved by means of a multipath connector of the xe2x80x9cZebraxe2x80x9d type by soldering, or by using an anisotropic conductive adhesive, or an anisotropic contacting foil (ACF). Such methods are technically entirely satisfactory when the LCD and the PCB are in the same plane. They are also satisfactory when, by choice or by necessity, the PCB is placed underneath the LCD, with, however, the risk of damaging the Zebra type connector paths if said connector is given too small a radius of curvature, as could be the case in a wristwatch with digital display having a case of very small thickness. In addition to the aforementioned risk, these methods also have the drawback of consuming relatively expensive intermediate materials (Zebra, ACF, etc.) and requiring a relatively long manufacturing time.
The present invention thus concerns a new method for connecting a LCD to a PCB, which is quicker, more economical and technically more reliable in that it does not rely on intermediate materials, but uses a laser beam.
The invention therefore concerns a method for connecting a printed circuit board (PCB) to the paths of the electrodes of a liquid crystal display cell (LCD) comprising, in a known manner, an upper plate, a lower plate and a sealing frame for confining said liquid crystal. The method comprises the following steps:
constructing the display cell while providing at least one extension of small width of the upper plate to support the electrode paths on its lower surface;
creating a connection zone by positioning said extension on contacts facing the PCB, and
focussing a laser beam on the connection zone, through the upper plate or in grazing incidence with respect to the lower plate to definitively establish the connections between the paths and the contacts of the PCB.
The method according to the invention thus no longer uses any intermediate materials and allows the connection operation to be achieved in a shorter time, which contributes to reducing the cost price of the final product.
According to a first embodiment, the upper plate of the LCD can include only a single extension and the PCB can be connected in the extension of the LCD and substantially in the same plane.
According to a second embodiment, the upper plate of the LCD can include at least two extensions and the PCB can be located under the LCD. In this case, the PCB advantageously has a recess for housing the lower plate such that the edges of the recess are flush with the lower surface of the upper plate. The product thereby obtained is compact and has good mechanical properties.